1. Field of the Invention
The present invention relates to methods and apparatus for operating self-propelled construction machines, and more particularly, but not by way of limitation, to methods and apparatus for operating slipform paving machines.
2. Description of the Prior Art
One known arrangement for a self-propelled construction machine includes a generally rectangular machine frame having a swing leg mounted at each corner of the frame and having a crawler track mounted at the free end of each swing leg. The crawler tracks provide the motive force for the construction machine. The mounting of the crawler tracks on the swing legs allows the crawler tracks to be repositioned in a horizontal plane relative to the machine frame for various reasons. For example, a slipform paving machine utilizing such construction may need to spread the forward extending swing legs in order to make room for a paving kit or other equipment supported from the machine frame. Also, it may be desirable during operation of the machine to relocate one or more of the swing legs and its associated crawler track to avoid obstacles. Also, the swing legs allow the crawler tracks to be repositioned for transport of the construction machine.
Various systems have been proposed for controlling the pivoting movement of the swing legs relative to the machine frame.
One system set forth in Swisher U.S. Pat. No. 3,970,405 provides that each track is individually raised off of the ground surface one at a time, and then the swing leg is manually pivoted to the desired orientation where it is fixed in place using turn buckles. Disadvantages of this system include the need to individually raise each track off the ground one at a time, and the need to realign the steering after adjusting the leg orientation.
Another approach is found in Aeschlimann U.S. Pat. No. 6,872,028 in which the swing legs are constructed as parallelogram linkages so that as the swing leg pivots in or out the steering direction of the crawler track remains unchanged.
Another solution is provided in Guntert U.S. Pat. No. 8,459,898 which provides a hydraulic ram between the swing leg and the machine frame which pivots the swing leg to a desired orientation. An automatic controller senses the change in pivot angle of the swing leg and maintains the steering angle of the crawler track in response to the change in pivot angle as the swing leg pivots.
The Aeschlimann and Guntert systems offer a solution to one problem present in the Swisher '405 patent, namely the need to individually raise each track off of the ground one at a time. However they create a new problem. Solutions like that of Aeschlimann or Guntert which maintain the steering angle of the crawler track while the swing leg pivots cause a sideways skidding of the crawler track across the ground surface. This sideways skidding contributes to wear of the crawler track and shaking of the machine, which is undesirable especially during paving. These machines are quite heavy and the footprint of the tracks is large, so the resistance to this skidding action is high.
Thus there is a continuing need for improvements in the arrangements for the control of the pivoting of swing legs of such automotive construction machines.